Dust Attenuation Curves in the Local Universe: Demographics and New Laws for Star-forming Galaxies and High-redshift Analogs

TL;DR

This study analyzes dust attenuation curves in 230,000 local universe galaxies, revealing their dependence on opacity and stellar mass, and provides new functional forms and a comprehensive catalog for diverse galaxy types.

Contribution

It introduces a new SED+LIR fitting method and characterizes the diversity of dust attenuation curves across galaxy populations, including high-redshift analogs.

Findings

Attenuation curve slopes vary widely, often as steep as the SMC curve.

Shallower curves are associated with more opaque, massive galaxies.

Average UV bump strength is about one-third of the Milky Way's.

Abstract

We study dust attenuation curves of 230,000 individual galaxies in the local universe, ranging from quiescent to intensely star-forming systems, using GALEX, SDSS, and WISE photometry calibrated on Herschel-ATLAS. We use a new method of constraining SED fits with infrared luminosity (SED+LIR fitting), and parameterized attenuation curves determined with the CIGALE SED fitting code. Attenuation curve slopes and UV bump strengths are reasonably well constrained independently from one another. We find that $A_{\lambda}/A_V$ attenuation curves exhibit a very wide range of slopes that are on average as steep as the SMC curve slope. The slope is a strong function of optical opacity. Opaque galaxies have shallower curves - in agreement with recent radiate transfer models. The dependence of slopes on the opacity produces an apparent dependence on stellar mass: more massive galaxies having shallower slopes. Attenuation curves exhibit a wide range of UV bump amplitudes, from none to MW-like; with an average strength 1/3 of the MW bump. Notably, local analogs of high-redshift galaxies have an average curve that is somewhat steeper than the SMC curve, with a modest UV bump that can be to first order ignored, as its effect on the near-UV magnitude is 0.1 mag. Neither the slopes nor the strengths of the UV bump depend on gas-phase metallicity. Functional forms for attenuation laws are presented for normal star-forming galaxies, high-z analogs and quiescent galaxies. We release the catalog of associated SFRs and stellar masses (GSWLC-2).